Cathodic protection has long been used to prevent or retard corrosion of oxidizable metallic items placed in contact with the earth, such as pipelines. Cathodic protection systems take advantage of the fact that different metals have different propensities for corrosion, and if items made of different metals are buried while being in electrically-conductive connection with each other, one of the items will corrode before or faster than the other one.
For example, if a steel pipeline is buried underground while being connected by electrical wire to a buried block of magnesium, the magnesium will corrode (i.e., oxidize) before the steel pipeline corrodes. In this example of a cathodic protection circuit, the steel pipeline acts as the cathode, and the magnesium block acts as the sacrificial anode. The pipeline may thus be protected against corrosion so long as it is connected to an appropriate number of anodes, and so long as the anodes are replaced when or before they have been totally consumed by corrosion. To enhance electrical conductivity between the anode and the cathode, and hence the efficacy of the cathodic protection system, the anodes commonly are installed with a buffer layer of carbonaceous filler material, such as charcoal or coke, separating the anodes from the surrounding soil.
There are several known methods of installing anodes. One method involves simply excavating a trench, placing one or more anodes in the trench, connecting the anodes by means of electrical wiring to the buried item desired to be protected against corrosion, and then backfilling the trench with soil. If desired, a layer of coke may be laid in the trench before the anodes are positioned, and then more coke may be added to cover the anodes before the trench is backfilled. Alternatively, the anode used in this method may be of a type which is pre-encased in a canister full of coke.
The trench method described immediately above has obvious disadvantages. It entails the use of trenching equipment such as a backhoe, and it results in an excavation considerably larger than the anode being buried. A correspondingly large amount of backfilling needs to be done after the anode is in place, and it will commonly be necessary to use compacting equipment to consolidate the backfill so as to prevent or minimize subsequent settlement of the backfill. These factors contribute to the time and expense involved in using the trench method.
Another known method involves augering a hole into the ground, lowering an anode into the hole, pouring coke or charcoal into the hole so as to surround the anode, and then backfilling the hole with soil from the top of the charcoal to the ground surface. This method has the advantage of causing considerably less disruption to the soil than the trench method, in that much less soil needs to be excavated and backfilled. As well, consolidation of the backfill often will not be necessary using this method. Accordingly, this method will often allow anodes to be installed more quickly and at less cost that using the trench method.
The augered hole method, as described above, has a significant drawback in that it can be difficult or impossible to use in sloughing or non-cohesive soils. In such cases soil from the sides of the augered hole may fall into the hole before the anode and charcoal can be placed in the hole, and some other method must then be used to install the anode. A further disadvantage of the augered hole system, regardless of the type of soil encountered, is that it can be difficult to keep the anode centered in the hole while the charcoal or coke is being poured in; i.e., the anode may become displaced such that the charcoal or coke does not surround the anode in a uniform thickness, or in some locations does not surround the anode at all.
The problem of sloughing or non-cohesive soils is addressed by a third known method of anode installation, namely the cased hole method. This is essentially the same as the augered hole method with the additional step of installing a cylindrical liner in the hole immediately after the hole has been augered out. The liner prevents sloughing of soil into the hole, so that installation of the anode and charcoal may proceed without complications. The obvious disadvantage of the cased hole method, however, is that the liner must be left permanently in the hole and cannot be re-used, thereby adding to the cost of each anode installation. A further disadvantage is that, as for the uncased augered hole method, it may be difficult to keep the anode centered in the hole to ensure that the anode is surrounded uniformly by charcoal or coke.
The prior art discloses several attempts to provide means for quicker and more efficient installation of anodes. U.S. Pat. No. 4,504,375, issued to Griffioen on Mar. 12, 1985, teaches a cylindrical casing containing an anode surrounded by carbonaceous material, with an electrical connection cable running from the anode to the outside of the casing. The lower end of the casing is formed with a sharp point so that the device may be driven into the ground using appropriate impactor equipment. The Griffioen invention eliminates the need for excavation and backfill during anode installation, and the nature of its assembly ensures uniform charcoal encasement of the anode. However, it has a significant drawback in that it must be left in the ground and has no re-usable components. Another disadvantage of this device is that its use entails some risk of damage to the anode due to shock loading as the device is being driven into the ground.
U.S. Pat. No. 4,626,330, issued to Farmer on Dec. 2, 1986, discloses an anode formed around an auger shaft so that it can be installed by rotating the auger shaft using appropriate rotating equipment. This device requires no excavation or backill, and avoids the risk of shock damage to the anode associated with driven anodes such as Griffioen. However, it has a significant disadvantage in that it does not permit installation of an anode in conjunction with a bedding of carbonaceous material. It has the further drawback of requiring an auger shaft which must be left in the ground and cannot be re-used.
For the foregoing reasons, there is a need for an apparatus and method which may be used to install cathodic protection anodes with carbonaceous bedding more economically and more efficiently than known apparatus and methods, in non-cohesive as well as cohesive soils, with minimal disruption to the soil and correspondingly minimal requirements for backfilling, and without risk of shock damage to the anode during installation. There is a further need for an anode installation apparatus and method entailing minimal need for components of such apparatus to be left permanently buried in the ground.